Photoelectric tube



Febf19, 1935.

P.` I L. SPENCER PHO'L'OELECTRIC TUBE Filed Nov. 25, 192s INVENTOR greater output than prior cells.

' formed by the local heating of the envelope.

Patented Feb. 19, 1935 Y PHOTOELECTRIC TUBE Percy L. Spencer, Medford, Mass., assignor, by

mesne assignments, to 01d Colony Trust Company, a corporation of Massachusetts Application November 23, 1928, Serial'No. 321,472

12 Claims.

This invention relates to photo-electric tubes or cells and to the manufacture thereof. An objectof my invention is to devise a cell whichwill be more sensitive to light and which Willhave a Another object of my invention is to devise a method of manufacture of a photo-cell which will be cheap, easy to carry out and result in a cell which is more sensitive than hitherto known.

The single figure in the drawing shows a photoelectric cell embodying my invention.

The cell comprises an envelope l of glass or other t-ransparent material. Projecting inwardly from each end are presses or pinches 2 in which is sealed a wire 3 running the entire length of the cell. This wire is preferably of nickel and constitutes the anode. Supported on the wire are globules 4 of magnesium, the purpose of which appears later. Sealed in press 2 are wires 14 and 15 supporting ring 5. This ring may be of magnesium or of any other metal supporting some magnesium.

Envelope 1 is connected to a suitable exhaust system and exhausted to as high a vacuum as possible. Thereafter wire 3 is heated by a current of electricity sufficiently to vaporize magnesium globules 4. At the same time, by means of a high frequency induction system, metal rings 5 are heated so that the magnesium there is also vaporized. VA mirror of magnesium is formed on the entire inner surface of envelope 1 in this manner, the envelope being hot in order to obtainA a desirable metal surface. Thereafter by means of a hand torch, a window outlined by line 7 is The magnesium sur' ce is volatilized at that spot, driven away an condenses in other portions of the cell.

In this manner, it is easily possible to obtain a window for the cell with a minimum of trouble. Of course the silver surface of the art may be used if desired. Asis well known, such a metallic surface is the basis upon which the photo-electrically.

active material is disposed.

In prior devices of this character, it has been customary to deposit the photo-electrically active material, usually an alkali metal or mixture thereof vsuch as potassium, rubidium or caesium', directly on the surface of this mirror. However, I

have found that by modifying this in accordance (Cl. Z-27.5)

such as rubidium bichromate. Instead of the rubidium compound, it is possible to use the caesium or potassium compound or any mixture thereof. The silicon may be replaced by another reducing agent if desired. The cell is now placed in an oven so that it is heated at a temperature below that required to vaporize the magnesium. Hence, the metallic layer on the inner surface is substantially undisturbed. At the same time, the capsule in appendix 10 is heated by high frequency currents so that decomposition and interaction occur between the chemicals. The ver'y rst result is the evolution of oxygen. The oxygen attacks the surface of the magnesium and converts it into magnesium oxide. Further heating of the capsule results in the evolution of metallic rubipears that the oxidized surface of the magnesium which is electro-negative to both the magnesium and alkali metal, has great aiiinity for the alkali metal and results in the latter settling upon the surface. Only enough alkali metal vapor to form 'dium or whatever alkali metal `is used. It apa very thin layer over the oxidized surface is necessary. During this treatment the cell is being exhausted so that there is only a comparatively small amount of oxygen and alkali metal vapor within the envelope 1. When the process is completed, the heating of the capsule is stopped, the capsule being sealed off; and the cell is evacuated in accordance with usual practice and sealed off at 21.

If desired, a quantity of gas may be introduced in order to increase the output. Although any of the rare gases have been used, I prefer to use a mixture of neon and helium containing 15% heliumand 'at a pressure of about 1,5 mm. mercury.

To obtain a contact with the inner cathode surface of the cell, a wire 3 is sealed into the wall and terminates in a metal cap 9 for outside connection.

In order vthat the alkali metal vapors be prevented from settling around the seal and destroying Ait and also` short circuiting the cell, I preferably arrange so that presses 2 have upstanding tubular projections 12 through'which the anode lead runs. A metal cap 13 closes the space between the wire and tube. If desired, anode 3 may be oxidized at the portions which come within tubular projections 12. If any alkali metal vapor does get in to/ the space, the interaction with the oxide coating results in an alkali oxide being formed on the wire.

A cell made in accordance with my method has been found to be much more sensitive than the average cells and has a substantially greater output. 'Ihe method of manufacture is easily carried out and allows of the formation of a window with a minimum of trouble. Furthermore, a superior cell is the result of such a method.

I claim: y

1. A photo-electric tube comprising a glass envelope, a layer of magnesium within said envelope, a compound on the surface of said magnesium, a photo-electrically active material on said compound and an electrode spaced from said photo-electrically active material.

2. A photo-electric tube comprising a glass envelope, a magnesium layer Within said envelope, a coating of magnesium oxide on the surface of said magnesium layer, a photo-electrically active material on said magnesium oxide, an electrode spaced from said photo-electrically active layer.

3. A photo-electric tube comprising a glass envelope, a magnesium layer within said envelope,

a surface coating of a magnesium compound on said layer, said surface coating being electronegative with respect to said magnesium, photoelectrically active material on said compound and an electrodel spaced from said photo-electrically active material.

4. A photo-electric tube comprising a lglass envelope, a magnesium layer within said envelope, a magnesium oxide coating on said layer, a layer of rubidium on said oxide coating and an electrode spaced from said rubidium layer.

5. The method of making a photo-electric tube cathode which comprises the steps of heating an exhausted glass container, introducing the vapor of magnesium within said container and causing it to condense on the inner surface thereof, locally heating said container in order to prevent the condensation of said vapor at certain portions of said container in order to form a window therefor, heating a quantity of an alkali metal oxidizing compound to produce, through decomposition of the compound, oxidizing gases and vapors, causing the said vapors and gases resulting from the decomposition of said oxidizing compound to interact with the magnesium layer, exhausting said container to a high vacuum and sealing it'.l 6. The method of making a photo-electric tube cathode which comprises the steps of forming a metal layer within an exhausted glass container, decomposing an alkali metal oxidizing compound and allowing resulting vapors and gases to interact with said metallic layer, said compound being heated in such manner as to evolve oxidizing substances rst Iand then the alkali metal, thereafter exhausting the tube to a high vacuum and sealing it.

7. The method of making a photo-electric tube cathode which comprises the steps of forming a magnesium layer Within an exhausted glass container, heating a mixture of silicon and an oxidizing alkali metal compound to produce vapors and oxidizing gases; causing the said vapors and gases to settle on and interact with the magnesium layer, exhausting said tube to. a high vacuum and sealing it. 8. A photo-electric tube comprising an exhausted container, a layer of alkali metal forming a photo-sensitive cathode, an anode within said tube, said anode being supported in atleast one press in said container, said press having a projecting tubular member surrounding a portion of said anode, said anode being oxidized along that portion of its length surrounded by said tubular member.

9. A photo-electric tube comprising an exhausted container, a layer of magnesium on the inner surface of said container, the surface of said layer having been oxidized, a layer of photoelectrically active alkali metal condensed on said oxidized layer, an anode, said anode being sealed in and supported by a press in said container, said press having a tubular member projecting inwardly into the tube, and surrounding a portion of said anode, said anode being oxidized along the length covered by said tubular-member.

10. 'I'he method of making a photo-electric tube cathode which comprises the steps vof introducing an easily oxidizable metal layer into a container, heating a quantity of an alkali metal oxidizing compound to produce, through decomposition of the compound, oxidizing' gases and alkali vapors, causing'the said gases and vapors to interact with said metal layer to oxidize the surface thereof and to deposit on said oxidized surface a layer of alkali metal.

11. 'I'he method of making a photo-electric tube cathode which comprises the steps of introducing an easily oxidizable -metal layer into a container, heating a quantity of an alkali metal oxidizing compound and a reducing agent to produce, through decomposition of the compound, oxidizing gases and alkali vapors, causing the said gases and vapors to interact with said metal layer to oxidize the surface thereof and to deposit on said oxidized surface a layer of alkali metal.

12. The method of making a photo-electric tube cathode which comprises the steps of introducing an easily oxidizable metal layer into a con- 

